Control device



May 13, 1947 K. M. MACKAY ETAL CONTROL DEVICE Filed April 30, 1945 .mmm

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m O JC .T An .m e h T Patented May 13, 1947 CONTROL DEVICE Kenneth M. lllackay and William J. Sims, Rugby,

England, assignors to General Electric Company, a corporation of New York Application April 30, 1945, Serial No. 591,030 In Great Britain November 3, 1944 (Cl. 20G-137') 3 Claims.

rihis invention relates to improvements in the control mechanism for electric heating and cook- .ing apparatus. Certain known control mechanism for this purpose consists of a switch of the quick acting type having a separate temperature sensitive element including a heating element connected in series or parallel tothe heating apparatus. Such a device while being suitable inv many cases lacks precision of control at the lower end of its rangs which in some circumstances is undesirable and the object of the present invention is to overcome this defect. To this end this invention consists in providing mechanism which reduces the internal lag of the operating member and which incorporates one or more switches so arranged that the control only operates kover a limited range including the temperature when accuracy is required. In carrying the invention into effect according to one form, we provide an expanding member operating a switch. The operating member preferably consists of :a wire which expands with increase in temperature. This increase is preferably obtained by passing an electric current through the member, which may be made of a high resistance alloy of relatively small cross-section thus having :a comparatively high resistance and a low thermal capacity making the member quickly responsive to the passage of current. Such a construction has the advantage compared with that in which the heater is separate from the operating member in that the time lag taken `for the heat to reach the operating member is eliminated and a more desirable characteristic is obtained.

For a more complete understanding of this invention, reference should be had to the accompanying drawing in which the single ligure is an elevation in section illustrating a, control device arranged in accordance with this invention and is adapted to control a pair of resistance units of a heating element.

In the drawing, I represents a panel to Which the frame 2 of the apparatus is rigidly secured. Within the frame are mounted two pairs of stationary contacts t, 4, and 5, 6, respectively adapted to be electrically connected by means of bridging members 1 and which are biased to closed position by springs 1a and 3a respectively. Contacts 4 and 5 are electrically connected by means of a pressure spring 9 which also makes contact with a hollow conducting tube I0. This tube is mounted in, but insulated from, a tube II rigidly secured to the frame 2. An annular ring I2 of insulating material is secured in the end of the tube I I and the conducting tube I slides through this ring. rihe end of tube IIJ is closed by means of a plug I3 of conducting material to the center of which a high resistance wire I4 is secured. The other end of this wire is secured to a member l5 which is adapted to slide in an insulating sleeve I6 secured in the other end of tube lll. A spring I1 is inserted between flanges on members l5 and It and' keeps the wire Ill taut. The posi- `tion of l5 can be adjusted by means of an insulating stud I3 slidably mounted in an aperture in the spindle I9 of the control knob 2E). The aperture is screw-threaded and contains a screw 2l which bears against the inner end of the stud I8 and controls the position of the stud. rThe spindle I9 also carries a cam 22 adapted during part of the movement of knob 2i? to hold the stem 23 of the bridging member 3 away from the contacts 5 and 6 against the action of the spring 8a. A member 24 secured to the tube I0 is adapted to .bear against the end of stem 24a of the bridging member 1 when the latter is engaging contacts 3 and 4. 25 and 25 are the heating elements to be controlled and 21 and 28 are the terminals connected to the supply system indicated by conductors 21a and 28a. The elements 25 and 26 may 'be the two heating units of a boiling plate and are preferably of the sheathed wire type.

In operation when current is switched on, a circuit is completed from terminal 21 through contacts 3, 1 and 4 to the spring member 9 and tube it. From there the current passes to plug i3, wire Iii, member I5, flexible conductor 29 to terminal '30 and from there through conductor 5I to heating element 25 and through conductor 32 to terminal 28. This completes the circuit of unit 25 which immediately commences to heat up. Bridging member 1 normally connects contacts 3 and ll being held in place by means of the spring TUI. The distance between the member 2li and the end of the stem Zea of the bridging member 1 is adjustable. As the unit 25 heats up the current passing through the wire I4 causes it to heat up and expand. The spring I1 forces the tube Ill axially carrying with it the member 24 and when a predetermined temperature has been reached this member engages the stem 24a and with it the bridging member 1, causing it to open the circuit through contacts 3 and 4, thereby cutting on the supply of current to the heating unit 25. As the wire is of small cross section it cools quickly and allows the bridging piece 1 to again complete the circuit. This cycle is repeated indenitely `so that the unit 25 can be kept at a comparatively even temperature. rI'he member 24 may be Chamfered or cam-shaped as that by adjusting it on the tube IU the amount of expension of wire lli before the member 24 opens the switch 'I may be varied, thereby allowing the unit to reach any desired temperature before its circuit is broken.

Where a greater heat is required from the heatiner means the knob 2Q is rotated until the cam 22 allows bridging member S to connect contacts 5 and G under the influence of its spring 6a. While the circuit of unit 25 is elo-sed there is now a circuit through unit 25. This circuit passes from terminal 27 through contacts 3, l, and 4 to member 9. Current then passes through ccntacts 5, 3, and to terminal 33 and through con ductor 34 to unit 2S and to terminal 28 through conductor 32. The two units are thus connected in parallel.

An arrangement such as described gives a ne control at the lower end or the heating range but it will be obvious that the circuit of unit 26 might be completed iirst with no control in it and the unit 25 there connected in circuit with a control arrangement as described, thus giving iine control at the upper end of the heating range.

While we have shown and described a particular embodiment of our invention, it will be obvious to those skilled in the art that various changes and modications may be made without departing from our invention in its broader aspects and we therefore aim in the appended claims to cover all such changes and modications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A control device comprising a nrst tubular member, a second tubular member slidably mounted in said first tubular member, a thermalh ly expansible and contractible lamentary member extending longitudinally within said second tubular member having one end secured to one end thereof, a spring interposed between the other ends of said second tubular member and Iilamentary member to tension the latter member and an abutment for the said other end of said lamentary member preventing any movement thereof in the direction of said abutment so that said second tubular member slides in opposite directions in said i'lrst tubular member when only as said lamentary member expands and contracts due to temperature changes, and switch means controlled by the sliding movements of said second tubular member.

2. A control device comprising a rst tubular member, a second tubular member slidably mounted in said first tubular member, a thermally expansible and contractible lamentary .member extending longitudinally within said second tubular member having one end secured to one end thereof, a spring interposed between the other ends of said second tubular member and lamentary member to tension the latter member and an abutment for the said other end of said rilamentary member so that said second tubular member slides in opposite directions in said first tubular member when said lamentary member expands and contracts due to temperature changes, switch means controlled by the sliding movements of said second tubular member, and means for adjusting the position of said abutment to shift said second tubular member and lamentaiy member as a unit with reference to said nrst tubular member.

3. A cont-rol device comprising a rst tubular member, a second tubular member sldably mounted in said first tubular member, a thermally expansible and contractible lamentary member extending longitudinally within said second tubular member having one end secured to one end thereof, a spring interposed between the other ends of said second tubular member and iilamentary member to tension the latter member and an abutment for the said other end of said lamentary member so that said second tubular member slides in opposite directions in said first tubular member when said lamentary member expands and contracts due to temperature changes, a member proj ectng from the said other end of said second tubular member with which said spring coacts, a switch having a xed contact and a movable contact biased to its closed position and said projecting member engaging said movable Contact to control its movement to and from its enga-gement with its said nxed contact.

KENNETH M. MACKAY, lWILLIAM J. SIMS.

REFERENCES CITED UNITED STATES PATENTS Name Date Smulski Aug. 7, 1934 Number 

